/*
 * Copyright 2002-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.bangcommunity.bbframe.common.utils.lang;

import java.lang.annotation.Annotation;
import java.lang.reflect.AnnotatedElement;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.bangcommunity.bbframe.common.utils.Assert;
import com.bangcommunity.bbframe.common.utils.reflect.BridgeMethodResolver;
import com.bangcommunity.bbframe.common.utils.reflect.ReflectionUtils;

/**
 * General utility methods for working with annotations, handling bridge methods (which the compiler
 * generates for generic declarations) as well as super methods (for optional &quot;annotation
 * inheritance&quot;). Note that none of this is provided by the JDK's introspection facilities
 * themselves.
 *
 * <p>
 * As a general rule for runtime-retained annotations (e.g. for transaction control, authorization,
 * or service exposure), always use the lookup methods on this class (e.g.,
 * {@link #findAnnotation(Method, Class)}, {@link #getAnnotation(Method, Class)}, and
 * {@link #getAnnotations(Method)}) instead of the plain annotation lookup methods in the JDK. You
 * can still explicitly choose between a <em>get</em> lookup on the given class level only
 * ({@link #getAnnotation(Method, Class)}) and a <em>find</em> lookup in the entire inheritance
 * hierarchy of the given method ({@link #findAnnotation(Method, Class)}).
 *
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @author Mark Fisher
 * @author Chris Beams
 * @author Phillip Webb
 * @since 2.0
 * @see Method#getAnnotations()
 * @see Method#getAnnotation(Class)
 */
public abstract class AnnotationUtils {

    /** The attribute name for annotations with a single element */
    public static final String VALUE = "value";

    private static final Map<AnnotationCacheKey, Annotation> findAnnotationCache = new ConcurrentReferenceHashMap<AnnotationCacheKey, Annotation>(
            256);

    private static final Map<Class<?>, Boolean> annotatedInterfaceCache = new ConcurrentReferenceHashMap<Class<?>, Boolean>(
            256);

    private static transient Logger logger;

    /**
     * Get a single {@link Annotation} of {@code annotationType} from the supplied annotation:
     * either the given annotation itself or a meta-annotation thereof.
     * 
     * @param ann
     *            the Annotation to check
     * @param annotationType
     *            the annotation type to look for, both locally and as a meta-annotation
     * @return the matching annotation, or {@code null} if none found
     * @since 4.0
     */
    @SuppressWarnings("unchecked")
    public static <T extends Annotation> T getAnnotation(Annotation ann, Class<T> annotationType) {
        if (annotationType.isInstance(ann)) {
            return (T) ann;
        }
        try {
            return ann.annotationType().getAnnotation(annotationType);
        } catch (Exception ex) {
            // Assuming nested Class values not resolvable within annotation attributes...
            logIntrospectionFailure(ann.annotationType(), ex);
            return null;
        }
    }

    /**
     * Get a single {@link Annotation} of {@code annotationType} from the supplied Method,
     * Constructor or Field. Meta-annotations will be searched if the annotation is not declared
     * locally on the supplied element.
     * 
     * @param annotatedElement
     *            the Method, Constructor or Field from which to get the annotation
     * @param annotationType
     *            the annotation type to look for, both locally and as a meta-annotation
     * @return the matching annotation, or {@code null} if none found
     * @since 3.1
     */
    public static <T extends Annotation> T getAnnotation(AnnotatedElement annotatedElement, Class<T> annotationType) {
        try {
            T ann = annotatedElement.getAnnotation(annotationType);
            if (ann == null) {
                for (Annotation metaAnn : annotatedElement.getAnnotations()) {
                    ann = metaAnn.annotationType().getAnnotation(annotationType);
                    if (ann != null) {
                        break;
                    }
                }
            }
            return ann;
        } catch (Exception ex) {
            // Assuming nested Class values not resolvable within annotation attributes...
            logIntrospectionFailure(annotatedElement, ex);
            return null;
        }
    }

    /**
     * Get all {@link Annotation Annotations} from the supplied Method, Constructor or Field.
     * 
     * @param annotatedElement
     *            the Method, Constructor or Field to retrieve annotations from
     * @return the annotations found, or {@code null} if not resolvable (e.g. because nested Class
     *         values in annotation attributes failed to resolve at runtime)
     * @since 4.0.8
     */
    public static Annotation[] getAnnotations(AnnotatedElement annotatedElement) {
        try {
            return annotatedElement.getAnnotations();
        } catch (Exception ex) {
            // Assuming nested Class values not resolvable within annotation attributes...
            logIntrospectionFailure(annotatedElement, ex);
            return null;
        }
    }

    /**
     * Get all {@link Annotation Annotations} from the supplied {@link Method}.
     * <p>
     * Correctly handles bridge {@link Method Methods} generated by the compiler.
     * 
     * @param method
     *            the Method to retrieve annotations from
     * @return the annotations found
     */
    public static Annotation[] getAnnotations(Method method) {
        try {
            return BridgeMethodResolver.findBridgedMethod(method).getAnnotations();
        } catch (Exception ex) {
            // Assuming nested Class values not resolvable within annotation attributes...
            logIntrospectionFailure(method, ex);
            return null;
        }
    }

    /**
     * Get a single {@link Annotation} of {@code annotationType} from the supplied {@link Method}.
     * <p>
     * Correctly handles bridge {@link Method Methods} generated by the compiler.
     * 
     * @param method
     *            the method to look for annotations on
     * @param annotationType
     *            the annotation type to look for
     * @return the annotations found
     */
    public static <A extends Annotation> A getAnnotation(Method method, Class<A> annotationType) {
        Method resolvedMethod = BridgeMethodResolver.findBridgedMethod(method);
        return getAnnotation((AnnotatedElement) resolvedMethod, annotationType);
    }

    /**
     * Get the possibly repeating {@link Annotation}s of {@code annotationType} from the supplied
     * {@link Method}. Deals with both a single direct annotation and repeating annotations nested
     * within a containing annotation.
     * <p>
     * Correctly handles bridge {@link Method Methods} generated by the compiler.
     * 
     * @param method
     *            the method to look for annotations on
     * @param containerAnnotationType
     *            the class of the container that holds the annotations
     * @param annotationType
     *            the annotation type to look for
     * @return the annotations found
     * @since 4.0
     */
    public static <A extends Annotation> Set<A> getRepeatableAnnotation(Method method,
            Class<? extends Annotation> containerAnnotationType, Class<A> annotationType) {

        Method resolvedMethod = BridgeMethodResolver.findBridgedMethod(method);
        return getRepeatableAnnotation((AnnotatedElement) resolvedMethod, containerAnnotationType, annotationType);
    }

    /**
     * Get the possibly repeating {@link Annotation}s of {@code annotationType} from the supplied
     * {@link AnnotatedElement}. Deals with both a single direct annotation and repeating
     * annotations nested within a containing annotation.
     * <p>
     * Correctly handles bridge {@link Method Methods} generated by the compiler.
     * 
     * @param annotatedElement
     *            the element to look for annotations on
     * @param containerAnnotationType
     *            the class of the container that holds the annotations
     * @param annotationType
     *            the annotation type to look for
     * @return the annotations found
     * @since 4.0
     */
    public static <A extends Annotation> Set<A> getRepeatableAnnotation(AnnotatedElement annotatedElement,
            Class<? extends Annotation> containerAnnotationType, Class<A> annotationType) {

        try {
            if (annotatedElement.getAnnotations().length > 0) {
                return new AnnotationCollector<A>(containerAnnotationType, annotationType).getResult(annotatedElement);
            }
        } catch (Exception ex) {
            // Assuming nested Class values not resolvable within annotation attributes...
            logIntrospectionFailure(annotatedElement, ex);
        }
        return Collections.emptySet();
    }

    /**
     * Find a single {@link Annotation} of {@code annotationType} from the supplied {@link Method},
     * traversing its super methods (i.e., from superclasses and interfaces) if no annotation can be
     * found on the given method itself.
     * <p>
     * Annotations on methods are not inherited by default, so we need to handle this explicitly.
     * 
     * @param method
     *            the method to look for annotations on
     * @param annotationType
     *            the annotation type to look for
     * @return the annotation found, or {@code null} if none
     */
    @SuppressWarnings("unchecked")
    public static <A extends Annotation> A findAnnotation(Method method, Class<A> annotationType) {
        AnnotationCacheKey cacheKey = new AnnotationCacheKey(method, annotationType);
        A result = (A) findAnnotationCache.get(cacheKey);
        if (result == null) {
            result = getAnnotation(method, annotationType);
            Class<?> clazz = method.getDeclaringClass();
            if (result == null) {
                result = searchOnInterfaces(method, annotationType, clazz.getInterfaces());
            }
            while (result == null) {
                clazz = clazz.getSuperclass();
                if (clazz == null || clazz.equals(Object.class)) {
                    break;
                }
                try {
                    Method equivalentMethod = clazz.getDeclaredMethod(method.getName(), method.getParameterTypes());
                    result = getAnnotation(equivalentMethod, annotationType);
                } catch (NoSuchMethodException ex) {
                    // No equivalent method found
                }
                if (result == null) {
                    result = searchOnInterfaces(method, annotationType, clazz.getInterfaces());
                }
            }
            if (result != null) {
                findAnnotationCache.put(cacheKey, result);
            }
        }
        return result;
    }

    private static <A extends Annotation> A searchOnInterfaces(Method method, Class<A> annotationType,
            Class<?>... ifcs) {
        A annotation = null;
        for (Class<?> iface : ifcs) {
            if (isInterfaceWithAnnotatedMethods(iface)) {
                try {
                    Method equivalentMethod = iface.getMethod(method.getName(), method.getParameterTypes());
                    annotation = getAnnotation(equivalentMethod, annotationType);
                } catch (NoSuchMethodException ex) {
                    // Skip this interface - it doesn't have the method...
                }
                if (annotation != null) {
                    break;
                }
            }
        }
        return annotation;
    }

    private static boolean isInterfaceWithAnnotatedMethods(Class<?> iface) {
        Boolean flag = annotatedInterfaceCache.get(iface);
        if (flag != null) {
            return flag;
        }
        boolean found = false;
        for (Method ifcMethod : iface.getMethods()) {
            try {
                if (ifcMethod.getAnnotations().length > 0) {
                    found = true;
                    break;
                }
            } catch (Exception ex) {
                // Assuming nested Class values not resolvable within annotation attributes...
                logIntrospectionFailure(ifcMethod, ex);
            }
        }
        annotatedInterfaceCache.put(iface, found);
        return found;
    }

    /**
     * Find a single {@link Annotation} of {@code annotationType} on the supplied {@link Class},
     * traversing its interfaces, annotations, and superclasses if the annotation is not
     * <em>present</em> on the given class itself.
     * <p>
     * This method explicitly handles class-level annotations which are not declared as
     * {@link java.lang.annotation.Inherited inherited} <em>as well as meta-annotations and
     * annotations on interfaces</em>.
     * <p>
     * The algorithm operates as follows:
     * <ol>
     * <li>Search for the annotation on the given class and return it if found.
     * <li>Recursively search through all interfaces that the given class declares.
     * <li>Recursively search through all annotations that the given class declares.
     * <li>Recursively search through the superclass hierarchy of the given class.
     * </ol>
     * <p>
     * Note: in this context, the term <em>recursively</em> means that the search process continues
     * by returning to step #1 with the current interface, annotation, or superclass as the class to
     * look for annotations on.
     * 
     * @param clazz
     *            the class to look for annotations on
     * @param annotationType
     *            the type of annotation to look for
     * @return the annotation if found, or {@code null} if not found
     */
    @SuppressWarnings("unchecked")
    public static <A extends Annotation> A findAnnotation(Class<?> clazz, Class<A> annotationType) {
        AnnotationCacheKey cacheKey = new AnnotationCacheKey(clazz, annotationType);
        A result = (A) findAnnotationCache.get(cacheKey);
        if (result == null) {
            result = findAnnotation(clazz, annotationType, new HashSet<Annotation>());
            if (result != null) {
                findAnnotationCache.put(cacheKey, result);
            }
        }
        return result;
    }

    /**
     * Perform the search algorithm for {@link #findAnnotation(Class, Class)}, avoiding endless
     * recursion by tracking which annotations have already been <em>visited</em>.
     * 
     * @param clazz
     *            the class to look for annotations on
     * @param annotationType
     *            the type of annotation to look for
     * @param visited
     *            the set of annotations that have already been visited
     * @return the annotation if found, or {@code null} if not found
     */
    @SuppressWarnings("unchecked")
    private static <A extends Annotation> A findAnnotation(Class<?> clazz, Class<A> annotationType,
            Set<Annotation> visited) {
        Assert.notNull(clazz, "Class must not be null");

        try {
            Annotation[] anns = clazz.getDeclaredAnnotations();
            for (Annotation ann : anns) {
                if (ann.annotationType().equals(annotationType)) {
                    return (A) ann;
                }
            }
            for (Annotation ann : anns) {
                if (!isInJavaLangAnnotationPackage(ann) && visited.add(ann)) {
                    A annotation = findAnnotation(ann.annotationType(), annotationType, visited);
                    if (annotation != null) {
                        return annotation;
                    }
                }
            }
        } catch (Exception ex) {
            // Assuming nested Class values not resolvable within annotation attributes...
            logIntrospectionFailure(clazz, ex);
            return null;
        }

        for (Class<?> ifc : clazz.getInterfaces()) {
            A annotation = findAnnotation(ifc, annotationType, visited);
            if (annotation != null) {
                return annotation;
            }
        }

        Class<?> superclass = clazz.getSuperclass();
        if (superclass == null || superclass.equals(Object.class)) {
            return null;
        }
        return findAnnotation(superclass, annotationType, visited);
    }

    /**
     * Find the first {@link Class} in the inheritance hierarchy of the specified {@code clazz}
     * (including the specified {@code clazz} itself) which declares an annotation for the specified
     * {@code annotationType}, or {@code null} if not found. If the supplied {@code clazz} is
     * {@code null}, {@code null} will be returned.
     * <p>
     * If the supplied {@code clazz} is an interface, only the interface itself will be checked; the
     * inheritance hierarchy for interfaces will not be traversed.
     * <p>
     * The standard {@link Class} API does not provide a mechanism for determining which class in an
     * inheritance hierarchy actually declares an {@link Annotation}, so we need to handle this
     * explicitly.
     * 
     * @param annotationType
     *            the annotation type to look for, both locally and as a meta-annotation
     * @param clazz
     *            the class on which to check for the annotation (may be {@code null})
     * @return the first {@link Class} in the inheritance hierarchy of the specified {@code clazz}
     *         which declares an annotation for the specified {@code annotationType}, or
     *         {@code null} if not found
     * @see Class#isAnnotationPresent(Class)
     * @see Class#getDeclaredAnnotations()
     * @see #findAnnotationDeclaringClassForTypes(List, Class)
     * @see #isAnnotationDeclaredLocally(Class, Class)
     */
    public static Class<?> findAnnotationDeclaringClass(Class<? extends Annotation> annotationType, Class<?> clazz) {
        Assert.notNull(annotationType, "Annotation type must not be null");
        if (clazz == null || clazz.equals(Object.class)) {
            return null;
        }
        if (isAnnotationDeclaredLocally(annotationType, clazz)) {
            return clazz;
        }
        return findAnnotationDeclaringClass(annotationType, clazz.getSuperclass());
    }

    /**
     * Find the first {@link Class} in the inheritance hierarchy of the specified {@code clazz}
     * (including the specified {@code clazz} itself) which declares at least one of the specified
     * {@code annotationTypes}, or {@code null} if none of the specified annotation types could be
     * found.
     * <p>
     * If the supplied {@code clazz} is {@code null}, {@code null} will be returned.
     * <p>
     * If the supplied {@code clazz} is an interface, only the interface itself will be checked; the
     * inheritance hierarchy for interfaces will not be traversed.
     * <p>
     * The standard {@link Class} API does not provide a mechanism for determining which class in an
     * inheritance hierarchy actually declares one of several candidate {@linkplain Annotation
     * annotations}, so we need to handle this explicitly.
     * 
     * @param annotationTypes
     *            the list of Class objects corresponding to the annotation types
     * @param clazz
     *            the Class object corresponding to the class on which to check for the annotations,
     *            or {@code null}
     * @return the first {@link Class} in the inheritance hierarchy of the specified {@code clazz}
     *         which declares an annotation of at least one of the specified
     *         {@code annotationTypes}, or {@code null} if not found
     * @since 3.2.2
     * @see Class#isAnnotationPresent(Class)
     * @see Class#getDeclaredAnnotations()
     * @see #findAnnotationDeclaringClass(Class, Class)
     * @see #isAnnotationDeclaredLocally(Class, Class)
     */
    public static Class<?> findAnnotationDeclaringClassForTypes(List<Class<? extends Annotation>> annotationTypes,
            Class<?> clazz) {
        Assert.notEmpty(annotationTypes, "The list of annotation types must not be empty");
        if (clazz == null || clazz.equals(Object.class)) {
            return null;
        }
        for (Class<? extends Annotation> annotationType : annotationTypes) {
            if (isAnnotationDeclaredLocally(annotationType, clazz)) {
                return clazz;
            }
        }
        return findAnnotationDeclaringClassForTypes(annotationTypes, clazz.getSuperclass());
    }

    /**
     * Determine whether an annotation for the specified {@code annotationType} is declared locally
     * on the supplied {@code clazz}. The supplied {@link Class} may represent any type.
     * <p>
     * Note: This method does <strong>not</strong> determine if the annotation is
     * {@linkplain java.lang.annotation.Inherited inherited}. For greater clarity regarding
     * inherited annotations, consider using {@link #isAnnotationInherited(Class, Class)} instead.
     * 
     * @param annotationType
     *            the Class object corresponding to the annotation type
     * @param clazz
     *            the Class object corresponding to the class on which to check for the annotation
     * @return {@code true} if an annotation for the specified {@code annotationType} is declared
     *         locally on the supplied {@code clazz}
     * @see Class#getDeclaredAnnotations()
     * @see #isAnnotationInherited(Class, Class)
     */
    public static boolean isAnnotationDeclaredLocally(Class<? extends Annotation> annotationType, Class<?> clazz) {
        Assert.notNull(annotationType, "Annotation type must not be null");
        Assert.notNull(clazz, "Class must not be null");
        boolean declaredLocally = false;
        try {
            for (Annotation ann : clazz.getDeclaredAnnotations()) {
                if (ann.annotationType().equals(annotationType)) {
                    declaredLocally = true;
                    break;
                }
            }
        } catch (Exception ex) {
            // Assuming nested Class values not resolvable within annotation attributes...
            logIntrospectionFailure(clazz, ex);
        }
        return declaredLocally;
    }

    /**
     * Determine whether an annotation for the specified {@code annotationType} is present on the
     * supplied {@code clazz} and is {@linkplain java.lang.annotation.Inherited inherited} (i.e.,
     * not declared locally for the class).
     * <p>
     * If the supplied {@code clazz} is an interface, only the interface itself will be checked. In
     * accordance with standard meta-annotation semantics, the inheritance hierarchy for interfaces
     * will not be traversed. See the {@linkplain java.lang.annotation.Inherited Javadoc} for the
     * {@code @Inherited} meta-annotation for further details regarding annotation inheritance.
     * 
     * @param annotationType
     *            the Class object corresponding to the annotation type
     * @param clazz
     *            the Class object corresponding to the class on which to check for the annotation
     * @return {@code true} if an annotation for the specified {@code annotationType} is present on
     *         the supplied {@code clazz} and is <em>inherited</em>
     * @see Class#isAnnotationPresent(Class)
     * @see #isAnnotationDeclaredLocally(Class, Class)
     */
    public static boolean isAnnotationInherited(Class<? extends Annotation> annotationType, Class<?> clazz) {
        Assert.notNull(annotationType, "Annotation type must not be null");
        Assert.notNull(clazz, "Class must not be null");
        return (clazz.isAnnotationPresent(annotationType) && !isAnnotationDeclaredLocally(annotationType, clazz));
    }

    /**
     * Determine if the supplied {@link Annotation} is defined in the core JDK
     * {@code java.lang.annotation} package.
     * 
     * @param annotation
     *            the annotation to check (never {@code null})
     * @return {@code true} if the annotation is in the {@code java.lang.annotation} package
     */
    public static boolean isInJavaLangAnnotationPackage(Annotation annotation) {
        Assert.notNull(annotation, "Annotation must not be null");
        return annotation.annotationType().getName().startsWith("java.lang.annotation");
    }

    /**
     * Retrieve the given annotation's attributes as a {@link Map}, preserving all attribute types
     * as-is.
     * <p>
     * Note: This method actually returns an {@link AnnotationAttributes} instance. However, the
     * {@code Map} signature has been preserved for binary compatibility.
     * 
     * @param annotation
     *            the annotation to retrieve the attributes for
     * @return the Map of annotation attributes, with attribute names as keys and corresponding
     *         attribute values as values
     */
    public static Map<String, Object> getAnnotationAttributes(Annotation annotation) {
        return getAnnotationAttributes(annotation, false, false);
    }

    /**
     * Retrieve the given annotation's attributes as a {@link Map}. Equivalent to calling
     * {@link #getAnnotationAttributes(Annotation, boolean, boolean)} with the
     * {@code nestedAnnotationsAsMap} parameter set to {@code false}.
     * <p>
     * Note: This method actually returns an {@link AnnotationAttributes} instance. However, the
     * {@code Map} signature has been preserved for binary compatibility.
     * 
     * @param annotation
     *            the annotation to retrieve the attributes for
     * @param classValuesAsString
     *            whether to turn Class references into Strings (for compatibility with
     *            {@link org.springframework.core.type.AnnotationMetadata} or to preserve them as
     *            Class references
     * @return the Map of annotation attributes, with attribute names as keys and corresponding
     *         attribute values as values
     */
    public static Map<String, Object> getAnnotationAttributes(Annotation annotation, boolean classValuesAsString) {
        return getAnnotationAttributes(annotation, classValuesAsString, false);
    }

    /**
     * Retrieve the given annotation's attributes as an {@link AnnotationAttributes} map structure.
     * <p>
     * This method provides fully recursive annotation reading capabilities on par with the
     * reflection-based {@link org.springframework.core.type.StandardAnnotationMetadata}.
     * 
     * @param annotation
     *            the annotation to retrieve the attributes for
     * @param classValuesAsString
     *            whether to turn Class references into Strings (for compatibility with
     *            {@link org.springframework.core.type.AnnotationMetadata} or to preserve them as
     *            Class references
     * @param nestedAnnotationsAsMap
     *            whether to turn nested Annotation instances into {@link AnnotationAttributes} maps
     *            (for compatibility with {@link org.springframework.core.type.AnnotationMetadata}
     *            or to preserve them as Annotation instances
     * @return the annotation attributes (a specialized Map) with attribute names as keys and
     *         corresponding attribute values as values
     * @since 3.1.1
     */
    public static AnnotationAttributes getAnnotationAttributes(Annotation annotation, boolean classValuesAsString,
            boolean nestedAnnotationsAsMap) {

        AnnotationAttributes attrs = new AnnotationAttributes();
        Method[] methods = annotation.annotationType().getDeclaredMethods();
        for (Method method : methods) {
            if (method.getParameterTypes().length == 0 && method.getReturnType() != void.class) {
                try {
                    Object value = method.invoke(annotation);
                    attrs.put(method.getName(), adaptValue(value, classValuesAsString, nestedAnnotationsAsMap));
                } catch (Exception ex) {
                    throw new IllegalStateException("Could not obtain annotation attribute values", ex);
                }
            }
        }
        return attrs;
    }

    /**
     * Adapt the given value according to the given class and nested annotation settings.
     * 
     * @param value
     *            the annotation attribute value
     * @param classValuesAsString
     *            whether to turn Class references into Strings (for compatibility with
     *            {@link org.springframework.core.type.AnnotationMetadata} or to preserve them as
     *            Class references
     * @param nestedAnnotationsAsMap
     *            whether to turn nested Annotation instances into {@link AnnotationAttributes} maps
     *            (for compatibility with {@link org.springframework.core.type.AnnotationMetadata}
     *            or to preserve them as Annotation instances
     * @return the adapted value, or the original value if no adaptation is needed
     */
    static Object adaptValue(Object value, boolean classValuesAsString, boolean nestedAnnotationsAsMap) {
        if (classValuesAsString) {
            if (value instanceof Class) {
                value = ((Class<?>) value).getName();
            } else if (value instanceof Class[]) {
                Class<?>[] clazzArray = (Class[]) value;
                String[] newValue = new String[clazzArray.length];
                for (int i = 0; i < clazzArray.length; i++) {
                    newValue[i] = clazzArray[i].getName();
                }
                value = newValue;
            }
        }
        if (nestedAnnotationsAsMap && value instanceof Annotation) {
            return getAnnotationAttributes((Annotation) value, classValuesAsString, true);
        } else if (nestedAnnotationsAsMap && value instanceof Annotation[]) {
            Annotation[] realAnnotations = (Annotation[]) value;
            AnnotationAttributes[] mappedAnnotations = new AnnotationAttributes[realAnnotations.length];
            for (int i = 0; i < realAnnotations.length; i++) {
                mappedAnnotations[i] = getAnnotationAttributes(realAnnotations[i], classValuesAsString, true);
            }
            return mappedAnnotations;
        } else {
            return value;
        }
    }

    /**
     * Retrieve the <em>value</em> of the {@code &quot;value&quot;} attribute of a single-element
     * Annotation, given an annotation instance.
     * 
     * @param annotation
     *            the annotation instance from which to retrieve the value
     * @return the attribute value, or {@code null} if not found
     * @see #getValue(Annotation, String)
     */
    public static Object getValue(Annotation annotation) {
        return getValue(annotation, VALUE);
    }

    /**
     * Retrieve the <em>value</em> of a named attribute, given an annotation instance.
     * 
     * @param annotation
     *            the annotation instance from which to retrieve the value
     * @param attributeName
     *            the name of the attribute value to retrieve
     * @return the attribute value, or {@code null} if not found
     * @see #getValue(Annotation)
     */
    public static Object getValue(Annotation annotation, String attributeName) {
        if (annotation == null || !StringUtils.hasLength(attributeName)) {
            return null;
        }
        try {
            Method method = annotation.annotationType().getDeclaredMethod(attributeName);
            ReflectionUtils.makeAccessible(method);
            return method.invoke(annotation);
        } catch (Exception ex) {
            return null;
        }
    }

    /**
     * Retrieve the <em>default value</em> of the {@code &quot;value&quot;} attribute of a
     * single-element Annotation, given an annotation instance.
     * 
     * @param annotation
     *            the annotation instance from which to retrieve the default value
     * @return the default value, or {@code null} if not found
     * @see #getDefaultValue(Annotation, String)
     */
    public static Object getDefaultValue(Annotation annotation) {
        return getDefaultValue(annotation, VALUE);
    }

    /**
     * Retrieve the <em>default value</em> of a named attribute, given an annotation instance.
     * 
     * @param annotation
     *            the annotation instance from which to retrieve the default value
     * @param attributeName
     *            the name of the attribute value to retrieve
     * @return the default value of the named attribute, or {@code null} if not found
     * @see #getDefaultValue(Class, String)
     */
    public static Object getDefaultValue(Annotation annotation, String attributeName) {
        if (annotation == null) {
            return null;
        }
        return getDefaultValue(annotation.annotationType(), attributeName);
    }

    /**
     * Retrieve the <em>default value</em> of the {@code &quot;value&quot;} attribute of a
     * single-element Annotation, given the {@link Class annotation type}.
     * 
     * @param annotationType
     *            the <em>annotation type</em> for which the default value should be retrieved
     * @return the default value, or {@code null} if not found
     * @see #getDefaultValue(Class, String)
     */
    public static Object getDefaultValue(Class<? extends Annotation> annotationType) {
        return getDefaultValue(annotationType, VALUE);
    }

    /**
     * Retrieve the <em>default value</em> of a named attribute, given the {@link Class annotation
     * type}.
     * 
     * @param annotationType
     *            the <em>annotation type</em> for which the default value should be retrieved
     * @param attributeName
     *            the name of the attribute value to retrieve.
     * @return the default value of the named attribute, or {@code null} if not found
     * @see #getDefaultValue(Annotation, String)
     */
    public static Object getDefaultValue(Class<? extends Annotation> annotationType, String attributeName) {
        if (annotationType == null || !StringUtils.hasLength(attributeName)) {
            return null;
        }
        try {
            return annotationType.getDeclaredMethod(attributeName).getDefaultValue();
        } catch (Exception ex) {
            return null;
        }
    }

    private static void logIntrospectionFailure(AnnotatedElement annotatedElement, Exception ex) {
        Logger loggerToUse = logger;
        if (loggerToUse == null) {
            loggerToUse = LoggerFactory.getLogger(AnnotationUtils.class);
            logger = loggerToUse;
        }
        if (loggerToUse.isInfoEnabled()) {
            loggerToUse.info("Failed to introspect annotations on [" + annotatedElement + "]: " + ex);
        }
    }

    /**
     * Cache key for the AnnotatedElement cache.
     */
    private static class AnnotationCacheKey {

        private final AnnotatedElement element;

        private final Class<? extends Annotation> annotationType;

        public AnnotationCacheKey(AnnotatedElement element, Class<? extends Annotation> annotationType) {
            this.element = element;
            this.annotationType = annotationType;
        }

        @Override
        public boolean equals(Object other) {
            if (this == other) {
                return true;
            }
            if (!(other instanceof AnnotationCacheKey)) {
                return false;
            }
            AnnotationCacheKey otherKey = (AnnotationCacheKey) other;
            return (this.element.equals(otherKey.element)
                    && ObjectUtils.nullSafeEquals(this.annotationType, otherKey.annotationType));
        }

        @Override
        public int hashCode() {
            return (this.element.hashCode() * 29 + this.annotationType.hashCode());
        }
    }

    private static class AnnotationCollector<A extends Annotation> {

        private final Class<? extends Annotation> containerAnnotationType;

        private final Class<A> annotationType;

        private final Set<AnnotatedElement> visited = new HashSet<AnnotatedElement>();

        private final Set<A> result = new LinkedHashSet<A>();

        public AnnotationCollector(Class<? extends Annotation> containerAnnotationType, Class<A> annotationType) {
            this.containerAnnotationType = containerAnnotationType;
            this.annotationType = annotationType;
        }

        public Set<A> getResult(AnnotatedElement element) {
            process(element);
            return Collections.unmodifiableSet(this.result);
        }

        @SuppressWarnings("unchecked")
        private void process(AnnotatedElement annotatedElement) {
            if (this.visited.add(annotatedElement)) {
                for (Annotation ann : annotatedElement.getAnnotations()) {
                    if (ObjectUtils.nullSafeEquals(this.annotationType, ann.annotationType())) {
                        this.result.add((A) ann);
                    } else if (ObjectUtils.nullSafeEquals(this.containerAnnotationType, ann.annotationType())) {
                        this.result.addAll(getValue(ann));
                    } else if (!isInJavaLangAnnotationPackage(ann)) {
                        process(ann.annotationType());
                    }
                }
            }
        }

        @SuppressWarnings("unchecked")
        private List<A> getValue(Annotation annotation) {
            try {
                Method method = annotation.annotationType().getDeclaredMethod("value");
                ReflectionUtils.makeAccessible(method);
                return Arrays.asList((A[]) method.invoke(annotation));
            } catch (Exception ex) {
                // Unable to read value from repeating annotation container -> ignore it.
                return Collections.emptyList();
            }
        }
    }

}
